16 – Desktop Fiber Laser: Colours Pt 4 The Rainbow’s End (50:12)

0:00welcome to another fiber laser learning lab today’s session is entitled the end

0:05of the rainbow because I’m going to be quite brutal and we’re going to close

0:10the session on color marking stainless steel today now hope it’s going to be

0:16quite informative because I’ve been working labora Slee for the past few days putting hundreds of samples through

0:22this machine trying to zoom in on some colors that satisfy one of the grades

0:30that we talked about last time in my color grading system now later on we

0:35shall be looking at these colors under the microscope because it is very important to you understand where and

0:42how these colors come about and some of the I suspect untried new and tested

0:49methods that I have exploited to try and get these colors into a position where

0:55they are durable and fast to produce that most of the colors that you have

1:02seen to date mainly in the D category of my listing now I’ve got a few of those

1:08here and what I’m going to do initially is to just show you the difference

1:14between a B C and D great colors now we’re very fortunate today that despite

1:20it being a cold day um it’s a lovely sunny day outside and we should be able

1:27to step out into the sunshine and look at the durability of these colors in natural bright sunlight I’ve also got

1:36beside me here some LED white lights

1:42although I could use fluorescent as well I think these three main variations of

1:48light will demonstrate the point that I’m going to make I hope you can forgive the lawnmower in the background my name

1:53is busy cutting his grass very fortunately I don’t have any grass because my dad was a bit of a

1:59philosopher and he told me when I was younger never have any more grass than your wife will mow now had a slight

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

2:06change of plan because I think it’s a benefit to pass on

2:12if possible some of the experience that I’ve gained over the past few days of

2:17playing with all these parameters it’s given me a tremendous insight into just

2:22the huge variety of opportunities you’ve got on this machine for controlling the

2:28power down onto the surface of the material colors is all about heat per

2:34unit area and you can change the heat per unit area in so many different ways

2:41with this machine anybody getting one of these machines for the first time it’s likely to be extremely confused by all these

2:48parameters much the same as I was with practice I’ve managed to begin to

2:53understand the relative importance of some of these factors now this is a Mopa

2:59laser machine now one of the most confusing things about this machine is

3:05all the pulse types we’ve got pulses that are 2 nanoseconds long and we’ve

3:12got pulses that are 350 nanoseconds long now you achieve these pulses by running

3:18the machine at these specific frequencies now 850 killer answers let’s

3:24just call that a thousand a thousand kilohertz is a million cycles a second

3:29so that means every cycle equals one

3:34microsecond now over here we’ve got 350 nanosecond pulse but you achieve that at

3:4125 kilohertz and that means a frequency of 40 microseconds so it’s 40 times

3:49slower than this but the pulse is 350

3:55nanoseconds this pulse is 2 nanoseconds so in terms of pulse duration this one

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

4:04is effectively about 170 times longer than that one so this pulse here is a

4:11hundred and seventy times roughly a hundred and seventy times more than that one in terms of duration but it’s

4:19repetition rate the number of times that that pulse gets put down there’s 40 times slower and this is the strange

4:27balancing act what I’m first going to do is just quickly show you in a in a

4:32sample patch the difference between these two so you just get a feeling for

4:39the damage that these two extremes can do to the material and there we go that

4:49was a two nanosecond pulse did it do much damage so yes it did a little bit

4:57of damage to the surface as you can see but I’m going to use this as a classic example of something else that I’m going

5:03to talk about in a minute which is the light sensitivity of the patent that

5:08we’ve produced now I’m going to rotate this very slightly backwards and forwards and as I rotate it backwards it

5:18turns to black and as I rotate it forward I get the pattern back again and then it

5:26turns to black it’s got a very narrow viewing angle and that narrow that viewing angle that’s less than plus or

5:32minus ten degrees so I’m now going to go to the other extreme and I’m going to put a 350 no no second pulse in and

5:39we’ll do exactly the same test that all I’m going to change is spot size I think

5:46you can see the difference in the power there you can hear it and you can see it that is a pretty powerful pulse I’m

5:52using a hundred percent power I’m using two thousand millimeters a second for doing all this work and we’ve also got a

6:00line spacing of a hundred microns there’s that first one if we hold it in

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

6:06to the light just right we can see that there’s not a lot of difference in the color they’re both silvery white and if

6:12I start rotating them look the first one disappears and goes to black and the

6:19next one well that can go a long way look and it

6:25still remains white

6:33so one of the main advantages of this longer pulses we get a more durable mark

6:38on the surface we’re not just tickling the surface we’re damaging the surface there is a lot more complexity in these

6:44numbers to be to be analyzed when we get on to another section but I just wanted

6:51to show you the difference between these two palp pulse what types to start with now percent power is quite a complex

6:57factor it’s not as it’s not just a simple a matter of saying well when I

7:02get hundred percent power I should get X amount and when I put fifty percent power down I’m going to get 50 percent

7:09of the effect it’s not that simple I’m afraid so something we talked about

7:14quite a lot when we spoke about focus was the shape of the energy the

7:21intensity of the light within the laser beam the beam goes down to a focus point like

7:26this and at this point out here up for the focus we’ve got a certain amount of

7:33power let’s call it twenty watts it doesn’t really matter but there’s a fixed amount of power taking place there and that power is spread in a Gaussian

7:41fashion across the laser beam and let’s say it looks like this well if we squash the beam down to a

7:48smaller dimension we’ve got the same amount of power under the beam and

7:53effectively what it does it causes the laser beam profile to do this it squashes it

8:01up now I’ve drawn it upwards because that’s the way you normally see a graph but in reality we also got to be looking

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

8:07at it this way around and saying well I have been profile looks like that the intensity of this light is not

8:13uniform across the beam and as we move further and further away from the focal

8:19point although you would normally expect the beam to get weaker in fact it

8:24doesn’t get weaker at all depending on the amount of power that you put into the laser beam you could have this power 10 15

8:33millimetres below the focal point that you could do damage with that is

8:39effectively what a hundred percent power look like it’s a sharp pencil that’s the best

8:45way that I can describe it to you it’s like writing with a very sharp pencil when you reduce the power to 20% you’re

8:53doing effectively the same as this so you’re making it very much a smoother distribution at the focal point I know

9:01it’s a silly analogy but it’s probably something that will stick in your mind we’ve got a sharp pencil at 100% and a

9:07blunt pencil at 20% so there are many different ways of reducing the power into the surface but one of them is

9:14probably not percent power if you want a sharp crisp image if you want a soft

9:20gentle application of heat then you reduce the percent power let me try and

9:26prove that to you did you see it that was what 20% power

9:31was if you look extremely hard with a

9:36little bit of imagination you might be able to just see something there it is look we catch it in the light just right

9:43and we can see some surface marking so what we just seen there are two effects

9:49not only have we got a long pulse which is effectively a soft blunt pulse

9:55I would like to imagine it as because it’s not a sharp crisp pulse like this one so we just blunted this blood pulse

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

10:05with a blunt pencil and that means we’re not putting very much power down onto the surface at all we’re not damaging

10:11the surface very much at all now my analogies are very crude but there are

10:17images that I’m carrying in my mind and have helped me to understand the relationship between these very complex

10:23factors okay so we’ve got our blunt and sharp pencil analog for power so my

10:30images for these this range of pulses it runs from delicate and sharp to if you

10:37like brutal and blunt that is like a scalpel and that is like a lumberjack’s

10:43axe you wouldn’t perform brain surgery with that but you might perform brain surgery with that it’s a scalpel and an axe as

10:51we said now there is a serious interplay between these numbers here the frequency at

10:58which the the repetition frequency in which at which these pulses occur and the linear speed now before we jump on

11:06to speed which has a direct relationship to this there’s something else you need

11:13to understand about these shapes and I’m going to use this one as a good example

11:18as we said this is roughly one

11:25microsecond okay a millionth of a second

11:32but this pulse is only two nano seconds long and nanosecond is one thousandth of

11:39this division so just here where my line is is that pulse and we travel for a

11:49whole microsecond a millionth of a second before we get another pulse and

11:55then another millionth of a second before we get the next pulse so there is

12:02a huge space relative to the pulse size in between the pulses to the next pulse

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

12:09so if you like that is Heat then that is

12:16cooling so we put a little teeny-weeny spike of

12:22heat in and we have a huge amount of time over which it gets a chance to cool

12:28how on earth are we ever going to get any heat into this product well the answer is really because of the thermal

12:36reactivity of the material itself the material cannot cool this quickly it can

12:42heat up and eventually if you heat it enough times in the same spot it will

12:47get hotter and hotter and hotter because it does not get a chance to call in between the poses now that’s an

12:53important fact to remember that if we can put more heat into the same spot we

13:01will gradually raise the temperature of that spot now we come back to speed so

13:08when we look at my chart of the various frequencies and pulse lengths you’ll find that across the bottom here we’ve

13:14got a ratio which is 588 500 500 435

13:20they’re all in the 4 to 600 to 1 ratio okay so we’ve got a very long cooling

13:28period for a very short heating period regardless of the pulse so with our two

13:33nanosecond pulse at 2000 millimeters a second even though we’re running at 850

13:42kilohertz which is nearly a million times a second we’re only putting down

13:47425 pulses per millimeter if we reduce

13:52the speed to a thousand millimeters a second we double it 850 which means

13:59we’re putting twice as much power into the same millimetre of stroke so the

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

14:06slower the speed the more pulses we can get I mean down at 100 millimeters a

14:11second but getting half thousand pulses per millimeter if we were to drop it

14:16down to one millimeter a second we’d have nearly a million pulses we’d have

14:22850,000 pulses per millimeter there is a very interesting relationship there in an important relationship between speed

14:30and this frequency and that’s what this table attempts to show so we can

14:40effectively increase the power and the effectiveness of this pulse by

14:45decreasing the speed at which we apply them because as we slow the speed we get

14:52more pulses per millimeter and that means we’re going to do more damage by

14:58running slower here’s the first one that you can’t see which is two thousand

15:03millimeters a second with a two nanosecond pulse okay so now we’ve reduced the speed to 500 so it’s a

15:11quarter of what it was before at two thousand you can actually see the scan

15:18speed this time now two things I hope you’ll notice first of all we’ve got some color in there now look this one is

15:28a quarter of the speed of that one so there it was silver and now you’re getting a hint of color in it because

15:35what we’ve done we’ve increased the power and we’re actually burning effectively the metal we’re producing a

15:41yellow oxide film on the surface in terms of light sensitivity about the

15:52same look they’re just about responding the same and then if I tip it the other way from the light now they’re both disappearing at about

15:59at the same time and here’s my chart for the 350 nanosecond pulse we’re only

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

16:04running at 25 kilohertz remember so therefore the repetition rate is very very slow so we’re only getting 13

16:12pulses per millimeter at 2000 but look

16:18we did this amount of damage with just 13 pulses per millimeter if I reduce it

16:24to 500 I’m now going to put 50 pulses per milliliter in so I don’t think it

16:30takes a genius to realize that we’re going to put a lot more power into the surface and we’re going to do a lot more damage you should both see it and here

16:41now we’ve turned it into a very dark gold because we’ve put huge amount more heat into the surface what have we done

16:48to the light durability it was pretty good before

16:57that’s extremely durable as far as angle of light is concerned as I said this has

17:04been a fascinating insight into learning about the machine hunting for these colors and understanding the way in

17:11which the parameters work so we’ve seen the way that speed linear speed can

17:18affect the amount of power that we put down in the horizontal direction if we

17:23want to change the power in the vertical direction we have the opportunity to do that as well if we’re doing engraving

17:31which we are most of the time because this is a scanning engraving machine then what we have the opportunity to do

17:37is to play with the line spacing this way the pitch between lines now at the moment on this test patch I’m using a

17:46hundred microns spacing I’ve got a 60 micron beam on here and so effectively

17:52there’s dead space between the lines that you’re looking at on this pattern here you can’t see that because your eye

17:59is just not capable of looking at that resolution we shall see under the microscope but not with your eye let’s

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

18:06forget that mistake that I made there in this horizontal direction with that one we increase the power to the surface by

18:12approximately a factor of four in the horizontal direction so what I’m now going to do is I’m going to modify this

18:18one by changing the line spacing from a hundred microns to 25 microns which

18:24again has a ratio of about four to one so we should find that we come out with

18:30more or less the same color as this one because we’ve got the same amount of power going down per square millimeter

18:42so I think that demonstrates to you clearly that changing the power ratio in

18:47one direction is not exactly the same as changing the power ratio in the other direction there are differences we get

18:55more effective heat change by horizontal change than we do by vertical change and

19:03that’s an important lesson that I learned when I was hunting for these colors so these very coarse glittery

19:10colors as you can see are much more resistant to light change now the final

19:17factor which sometimes has very little effect it’s the hatch pattern so these are the

19:25important factors just here we’ve got this little pattern we’ve got the opportunity to change this type of

19:31hatching let’s just go from the standard lines are the fly back and the blue

19:37lines are the actual cut so in this particular instance we’ve got a cut which is always in that direction

19:44okay it’s called a uni directional cut

19:50we have the opportunity here of a bi-directional cut you’ll see there’s got red lines at the end which means

19:56that we’re not cutting and so we’re cutting in that direction and that direction that’s bi-directional scanning then

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

20:04we’ve got this really strange pattern here which I don’t know what the value of it is but hey it’s it’s there if you

20:11need it I’ve found it’s of no value to you for producing colors because you get tremendous change in the energy density

20:18as you work towards the center of the pattern the heating effect these are things you’ll have to find out for yourself but the critical one which is

20:26very useful once you’ve got one of these patterns selected then let’s choose that one which is the bi-directional scanning

20:32which is slightly faster than the unidirectional scanning but it’s it’s negligible as this thing here if we tick

20:41this box here crosshatch what that will do that will do a series

20:48of lines like that and then it will do a series of lines like that and that’s a

20:53very useful pattern which I’ve discovered for producing couple now in the last session I spoke about my color

20:59grading scheme which I was going to use to judge the success or failure of each

21:05one of the patches that I was making and I’ve refined it quite a lot since the

21:12last session and so what I’m saying here now is my a grade I need a very wide

21:18viewing angle greater than plus or minus 60 degrees and that’s with all light

21:25sources now today we’re likely to be checking it with a halogen light an LED

21:31light and daylight so that’s a pretty reasonable mix I have got florescent

21:37light in here but fluorescents are so many different colors that you know we’re gonna discount those at the moment

21:43when we just go with the three main sources of light that you’re likely to find these being exposed to now color

21:49fidelity is whether the color remains the same for all light sources for

21:56instance LED light has got a very narrow spectral range whereas daylight is wide

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

22:04and halogen light is a close approximation to daylight so we’re

22:09likely to see significant color change with LED lights a very important factor

22:17for me really decides whether these colors are good or bad is whether they can be put down quickly I mean this is

22:24not untypical of the sort of size image that you might want to work on I had to

22:31give up on this Moe village after about half an hour because that’s as far as it got we’re here the gold and the white or

22:38latte color we’ve got one minute twenty five and one minute forty eight they’re

22:43completely acceptable production times for an object that size all my little test squares have been rationalized to

22:51one square centimeter now regardless of whether that’s got any

22:57engraving in it or not one square centimeter is one square centimeter if

23:04you want to work out how long it’s going to take for this image to do you’re just going to have to put a little average

23:10rectangle around it and work out how many square centimeters are in there so this image for example is on average

23:16let’s just have a quick assessment a little bit dealing a little bit out so that’s roughly 6 centimeters 6

23:23centimeters by about 5 6 is a 30 square centimeters so if it takes five seconds

23:30per square centimeter and we’ve got 30 of them that’s going to take about just over two minutes so that’s just one

23:38color I’ve now got to add the area for each one of these other colors that I

23:43choose to put in here as well so but the time I’ve filled in all these here that

23:48could take five or six minutes to do is that acceptable could I charge out at a rate which would allow me to get a good

23:55recovery on this machine that’s a decision that you will have to take but it all depends on the speed of which you

24:01can put the colors down that’s production izing these colors so that they become useful so the factors for

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

24:07the other grades are similar but for instance a B grade instead of plus or

24:12minus 60 degrees I’ve nominally chosen plus or minus 30 degrees based on my experience it’s very likely that they

24:21could be as much as plus or minus 60 degrees they could be a grade viewing but they could be incredibly long as far

24:29as production time is concerned which throws them out of the a grade and puts

24:34them into a B grade where you may want to use them it’s up to your judgment as to whether or not it’s cost-effective C

24:40grade and degrade very similar except that C grade have got a little bit more

24:48viewing capability than a D grade which is very limited at about plus or minus ten degrees and to be honest most of the

24:56colors that you’re going to encounter from other manufacturers who tagged the

25:03color chart as you know the best thing since sliced bread hmm it’s not that good because you know

25:11I wouldn’t buy a machine based on something that I would classes degrade colors I’ll know user for examples to

25:18look at these various grading it’s gold on the end has turned orange the kingfishers blues in the middle are more

25:25green that mode is not bad so that’s holding its color but it goes

25:32look I only got to turn it by a very small amount of angle and it all changes

25:37now that’s quite nice orange on the end isn’t it I thought that was a gold but here in

25:44sunlight is definitely orange very

25:49quickly you can see how easily they’re all black now almost except with the

25:55gold one now let’s just rotate them around very very gently look at the color coming in and then all the color

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

26:04disappearing that’s why I call those rubbish I mean there’s a big great

26:10colors and let’s rotate the round and it’s quite a few of those that you see

26:16are pretty robust there are no way rotated

26:32and these are got quite a quite a wide viewing angle

26:40so we take a look at these in white light LED light we can see the chameleon

26:50color on the end there which is a mocha Gold come they’re moderately robust

26:59those colors but the problem is time in

27:06white light I mean these colors don’t look very much different than what they do in daylight

27:21sadly that’s it that check color palette very very limited Browns Silver’s golds

27:31or black pink in a move so don’t get

27:36excited to convert my conclusions about colors on stainless steel at least I’m

27:44going to run this little program in real time for you so settle down with a cup of coffee and off we go

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32:11cool okay so that took about four and a half minutes and you can see my colors

32:21are pretty good they um they don’t change I move it around and this is in

32:29white light let’s go and have a look at in daylight so if it gets some Sun onto

32:35it then go we’re now in Nice sunlight

32:52well since I selected my color palette originally my a grade color palette I’ve been a bit more brutal with it and

32:59I’ve reduced it down to probably only about eight or ten drab colors well I

33:05say drab you’ve got some golds I’ve got some coppers some gray come green yeah I

33:13mean there’s a reasonable range there but it’s nothing like what you’re being

33:19sold and as you saw when this was being produced silver that silver around the

33:25outside that whitey silver is a nice rapid color to produce and you could use

33:31that on stainless steel it shows up very well as you can see but and gold as well

33:37also shows up well but apart from those two main colors I can’t see that you

33:43need many more for engraving texts on something but we’re gonna start looking

33:49at the degrade colors now this is I think without any surprise a gold that’s

33:5750 times magnification this is 400 times no surprises there hints of green but

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

34:05mainly yellows and rates net result you

34:11get what you see on the screen there’s no variation in depth so let’s take a look at the next one a bit of a sky blue

34:17game as I fiddle with the focus the color is just in the film itself in the

34:23oxide film on the surface next one is Kingfisher blue slightly different patination no they’re all everything’s

34:30at one depth there you just fiddle with the focus but nothing changes focus as I

34:35go up and down by one or two microns even now this came out as a salmon pink and sure enough I think you get what you

34:43see on the screen it’s a mixture of yellows and pinks but the predominant color when you look at it as salmon pink

34:50I think with more or less seen that pattern before in another bloom difficult to say where the focus is I

34:55think the focus is just about there so that’s the dark maroon color but

35:01again it’s flat run with the laser again twice and you get

35:08what you say which is blue okay so that’s a quick look at the C and D great

35:13colors which we’re not really interested in well I’m not interested in let me be fair about it what we’re gonna look at

35:21now is really my eighth-grade colors now the great thing about this color chase that I’ve been on is that they seem to

35:27be so much that people have not discovered about these colors or if they

35:33have discovered them they decide that they’re not worth pursuing or they’re rubbish the work that I’ve done has

35:39allowed me to discover three different basic types of color well I say types I

35:46mean textures you’ve now seen those that I disparagingly called D grades they are

35:52basically the principle of thin film interference which people have

35:58discovered to the eighth degree the colors that I’m interested in still using the thin film interference

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

36:03principle but looked a in a completely different way what you see on the screen

36:09there looks like I don’t know a piece of pink gravel well that’s exactly almost

36:16what it is it’s a disrupted surface which causes the light to change in so

36:23many different directions the thin film that’s on that surface cannot be pink

36:29there is no pink oxidation color so the only reason we’ve got pink is because

36:36there is already a mix of white light coming out to the to the microscope

36:43before it even reaches our eyes now look at the amount of black in there there is

36:49no indication of black when we look at that with the naked eye we only see a

36:55predominance of pink so that’s a gravel

37:00effect and we can look at that that’s looking at it at 50-times magnification if we just bump that up to 400 and take

37:08a look at it now I can’t get it in focus because there are so many there’s so much change of focal depth let’s come in

37:15and Ray is the table up so we picked the high spots up first in focus and here we go

37:23look we’ve got some high spots here coming into focus and then we’ll go up a

37:29little bit more and now we’ve got the stripes at the bottom of the valleys okay so that’s a three dimensional

37:37pattern you’ve got two forms of color mixing on that surface now the first form of light that you’re

37:42seeing there is from the tungsten lighting in the microscope you’ve got thin film interference off

37:49the surface which is creating the different colors yellows pinks and blues

37:54the flat surface at the bottom that lovely canary yellow that lovely pink

38:00they’re not in the color tempering range the only reason we can see them is

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

38:06because we’ve got an interference pattern which is affecting the light before even hits our eyes that’s what

38:13hits the microscope but the time it hits our eyes all those colors are Blumer

38:19ated and further interfered with and our eyes only see and the best I can show

38:25you is that that’s 50 times magnification by the time we see it’s 1 times magnification this surface is

38:32totally unpredictable in a strange sort of way it’s chaos here we’re getting

38:38variation in the thickness of the film superimposed on variation that we caused

38:43to the surface of the material so we’ve got ripples here like you see on the

38:48sand when that when the tide goes out that’s the second type of interference

38:55pattern that we’re perceiving with our eye there is a third one which I’m not sure that anybody has ever explored

39:01before and that’s something that I accidentally came across and revealed to

39:06you at the end of the last session now I’ve pursued this quite intensively

39:13because this is where the 8th grade colors really exist this as far as I’m

39:19aware is not something that people have ever been doing before to get color on

39:25stainless steel now he’s a gold where is the gold color coming from well

39:32it’s coming from the surface of the these little squares now this is not an

39:37area of science that I’ve seen anybody else working on discovering using

39:45exploiting what you’re seeing here is to the naked eye a lovely glittery gold

39:51what we’ve got here is a 60 micron laser beam and what we’ve got here is a 200 micron

40:00spacing and in between that grid we’ve created a heating effect on the surface

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

40:05now if you look at the color of each one of those squares you’ll see that what

40:10we’ve actually done we’ve created a flat thin film interference pattern on each

40:15one of those we’ve created a color which is pink yellowy

40:22whatever it is it hits the eye as a sparkly gold and it’s viewable from all

40:29sorts of directions and I think that’s purely because we’ve exploited the

40:35principle that we started off thinking about which is a cellular structure

40:41although they’re nano cell structures on a butterfly wing these are bigger but

40:48they’re exploiting the same effect we can go and look at that a little bit closer a lot closer at 400 Meg as I

40:55write use this image up and bring it into focus look at the black lines around the edge of the square that’s the debris on the side of the

41:01beam now carry on raising the focus up and you’ll see the surface come into

41:07focus and then I’ll raise it up more and

41:13you’ll see that the beam groove then coming into focus there so there’s a lot

41:18of depth in that picture now that’s not an incredibly powerful laser beam it’s one of

41:25the power beams it’s 100 burn a second pulse so it’s it’s in the fairly

41:31powerful region but it’s not certainly one of them powerful beams in fact I’ll tell you

41:36what let’s go and look at a powerful laser beam now this is silver 400 we’ve got

41:45two thousand millimeters a second speed and yet we’re only running at 25

41:51kilohertz frequency so what you’re able to see here is individual pulses and

42:03look at the metal that’s splashed up around each one of these pulses as soon

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

42:09as the liquid stainless steel hardens and it must have been liquid to produce these blobs we get a film an oxide film

42:20that is created on the surface as I mentioned to you probably in an earlier session from all the reading that I’ve

42:26done this oxide film forms within a few nanoseconds of the metal being exposed

42:33to oxygen so there will always be a film of some sort on the surface of stainless

42:38steel because of the interaction of chromium and oxygen and that effectively

42:44is freezing the color into the surface we’ve got the melted surface at the bottom of the laser beam and we’ve also got

42:52that surface there which is an undisturbed surface of the base material

42:57that has not been cut or melted and what you’re seeing there is the heating

43:04effect of the beam all around that little flat section it is caused its own

43:11thin film interference pattern of orange so there is a flat film interference

43:18pattern and the others are some three-dimensional pattern there is no green in the natural oxide colors so the

43:26only way that you can get green is by an interference pattern but of course those

43:32cauliflower shapes as I described them are not sticking up their little pits so

43:38you’ve got reflection off the inside of each one of those pits which is doing strange things to the interference

43:45patterns of light coming off surface and by the time it reaches your eye it looks like silver glittery silver

43:51now that I’m moving it to this sort of technology this is not predictable this

43:57is total chaos so there is little or no predictability to the color that I’m

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

44:04going to get it depends on the damage that I do to the surface and the heat that I put into the surface and the heat

44:10that I’m leaving behind in this residual undamaged area so let’s take a quick

44:16look at a few more of these colors so I will drop the magnification down to 200 so that we can see things quite quickly

44:22I’m just zooming in I’m just moving the focus around just so that you get an idea of the fact that there is quite a

44:28lot of variation in the depth of these things that’s a sort of a a latte color very light thorn it’s it’s mmm it’s on

44:37the edge of a bitter e gold but it’s it’s a little bit less than a gold now

44:43isn’t that beautiful now that’s a meet gold it’s quite a light a bright gold but you’ve got color

44:54in the beam as well there that’s an 8 known a second beam so in not doing as much damage with the beam itself and

45:01that’s why we can’t see the striations in the bottom of the laser beam because these are running at 250 kilohertz and we’re

45:09running the whole thing at 600 millimeters which is quite slow really relatively speaking but look here we’ve

45:16got enough heat to produce blue around the h of our square so that’s that’s one

45:24of the very fast Gold’s that I can produce takes about 2.9 or 3 seconds per

45:32square centimeter so this is exactly the same settings as the previous one except

45:37the speed has been changed from 600 to

45:43400 so in going down to 400 we’ve actually allowed more pulses per

45:49millimeter and we’ve had a greater heating effect so had gold has now

45:54changed into a copper color and maybe you could see that in the redness of the beam and that’s what’s

46:02probably causing the effect when it gets to the eye I hope to don’t me love this

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

46:09one this is like a almost a modern artwork this is actually a this actually comes

46:16out as a very very dark gold almost a brown now here’s another lovely silver

46:23and remember it’s not dissimilar to the silver that we first saw because this

46:30again looks like a field of collie flowers I mean this again is done with a

46:36maximum power laser beam 350 nano second beam but it’s running very slowly at 25

46:43kilohertz but we’re also running at quite high speed a thousand millimeters a second which is why you can see the

46:50spacing between the pulses so we’ve still got gold squares in there but we

46:56get no hint of gold when it meets our eye all we see is silver despite there being a lot of green in

47:03there and not much right now here we’ve got something that’s completely different to the eye this comes out as a

47:11smooth gold although this is very fast to produce at nine point five seconds it

47:18is not entirely durable as far as the viewing angle is concerned so I think I

47:26demoted this to a b-grade now you’ve seen this before because this

47:33is a silver in fact I have to say that to the eye this looks very white as

47:38opposed to silver should it does it look white not really so between physics and

47:47your brain there’s something weird going on okay any guesses as to what that

47:53might be in most likes this looks like a dark

48:01gray and it’s the dark gray that are used on the butterfly wing in other

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

48:08lights it’s got a little hint of brown in it this is definitely an iridescent color

48:14and yet can you see any hint of gray on that picture or any hint of brown as I

48:22said to you earlier this is chaos in action now most of the others as you

48:27have seen have been crosshatch pattern now this one isn’t a crosshatch pattern and it produces a matte finish any guess

48:37as to what the color might be jet black

48:44no it’s not dark gold that again is

48:51something you see on the butterfly wing so that’s enough of colors I think I’ve

48:57done enough research I think I’ve done enough discovery to set you guys on a

49:03trail if you wish to follow any of these directions and look for colors for

49:09yourself there are some new avenues here which I’m fairly confident have not been

49:14discovered before now the other interesting thought is for those guys

49:20with a q-switched laser looking at the very high powers and slow speeds and

49:27relatively low frequencies of some of these settings it is very possible that

49:33you might be able to use this technique to find colors on a q-switched laser I haven’t got a q-switched laser so I

49:40can’t experiment with it so I’m gonna leave this problem with you now I am NOT

49:47the user of this machine bear in mind I only play with this machine I get

49:53tremendous enjoyment from this machine and what you do with it is up to you

49:58so I think that’s a very convenient place to stop at this moment in time and say thank you very much for your

50:03patience and I’ll catch up with you in the next session where we will I promise not be

50:09touching colors